When a person's heart is in ventricular fibrillation, death is imminent. In ventricular fibrillation, the heart cells that stimulate the heart muscles are not coordinated so that although they stimulate the muscles, they produce rapid, erratic excitation without coordinated contraction of the ventricle. There is no effective simultaneous action to cause the heart to beat in a rhythmic fashion. To avoid death, immediate defibrillation is essential.
Defibrillation is achieved by delivering to the heart cells, enough voltage to override the erractic voltages in the fibrillating heart so that they can rearrange themselves with order. That action is called "repolarization". In this "repolarized" condition no heart action of any kind occurs for a peiod of three to eight seconds. After this three to eight seconds period, the heart cells arrange themselves to either fibrillate again or start a coordinated effort to beat on rhythm. If they fibrillate again, it is necessary to defibrillate them again, usually with more power. It may be necessary to do this several times before the heart cells arrange themselves to coordinate and beat in rhythm.
Defibrillation by high voltage is the accepted procedure today. Heavy duty equipment is required to deliver a very severe electric shock to the patient. The shock is delivered by placing two large paddle-type electrodes, each about three inches in diameter, at selected locations on the chest. By pressing down hard on the electrodes to make good electric contact with the skin, and by pressing a button provided on one of the paddle electrodes, the system is triggered so as to deliver the shock. The electrical shock is very abrupt; several thousand volts are impressed across the electrodes in a few milliseconds. In accordance with this procedure, in theory if the patient is given a large enough shock, some of it will pass through the heart and achieve repolarization. However, all the other muscles and nerves in the large area between the electrodes are also stimulated by the intense electrical shock, causing tremendous body flailing and thrashing.